Getting full path will fail if texture name in the plist is without relative path.

Resources-
|
Particles-
|
a.plist(texture name is `a.png`, just a file name without relative path)
a.png

a.plist and a.png are at the same directory.
When `CCParticleSystem::initWithDictionary` is invoked, the second parameter `dirname` will be `Particles/`.
The `Particles/` will not be inserted before texture name.